First of all please note that the temperature of 273 K is equal to `0^(@)C` and it melting point of ice (to form water) at the same temperature. Another point to be noted is that the latent heat of melting of ice (or fusion of ice) is `3.34 xx 10^(5)` joules per kilogram. Now, ice at 273 K (or `0^(@)C`) is more effective in cooling a substance than water at the same temperature of 273 K (or `0^(@)C`) because for melting, each kilogram of ice takes `3.34 xx 10^(5)` joules of its latent heat from that substance and hence cools the substance more effectively. On the other hand, water at the same temperature of 273 K (or `0^(@)C`) cannot take away any such latent heat from the substance and hence does not cool it more effectively.
